PLANT COMMUNITIES OF CULTIVATED FIELDS OF THE PODLASKI PRZEŁOM BUGU MESOREGION PART 5 . ROOT CROP COMMUNITIES OF LIGHT SOILS

This present paper, focused on root crop communities of light soils, is a part of the wide range characteristics of segetal communities of the Podlaski Przełom Bugu (Podlasie Bug River Gorge) mesoregion. On the basis of 160 phytosociological relevés made according to the Braun Blanquet method, phytocenoses re presenting the Panico-Setarion alliance were distinguished. Most often, patches of the association Echinochloo-Setarietum were re corded in the study area. Heterogeneous habitat conditions affect its floristic diversity. Two subassociations of the phytocenosis, di vided according to the species composition into 9 lower syntaxa, were identified on light soils. The following subassociations were distinguished: Echinochloo-Setarietum setarietosum glaucae in a typical variant and a variant with Juncus bufonius, both with subvariants with Digitaria ischaemum, as well as a typical variant of Echinochloo-Setarietum typicum, a variant with Juncus bufonius and a subvariant with Oxalis stricta in the typical and wet va riant. Another association found in root crops on light soils of the Podlaski Przełom Bugu mesoregion is Digitarietum ischaemi. Its patches were observed in cultivations on light, acidic, poor soils. The characteristic feature of this community is the occurrence of numerous acidophilous species. In habitat conditions typical for the Podlaski Przełom Bugu mesoregion, Digitarietum ischaemi is differentiated into the typical and wet variant. Quite frequent pat ches of the Setaria pumila-Setaria viridis community were noted in intermediate habitat conditions, between those characteristic for Digitarietum ischaemi and Echinochloo-Setarietum.


INTRODUCTION
The floristic composition of agrophytocenoses is determined by agricultural practice and natural conditions.Root crop communities are formed under the influence of high fertilisation, also including organic fertilisation, and crop protection agents used.Their characteristic feature is a large share of nitrophilous and thermophilic species.
In connection with changes in the crop structure and a growing share of cereal crops, as well as the increasing area of fallow land in the study area, root crop communities are less and less frequently found and they occupy small areas.
The purpose of the study was to demonstrate the floristic and phytosociological diversity of communities which develop in agrophytocenoses of the Podlaski Przełom Bugu mesoregion.
This paper is a continuation of the characteristics of plant communities of agrocenoses of the Podlaski Przełom Bugu mesoregion (S k r z y c z y ń s k a and R z y m o w s k a , 2005; R z y m o w s k a and S k r z y c z y ń s k a , 2006a, 2006b, 2006c).The study area and methodological assumptions, including abbreviations and numbers of localities used in the tables, are presented in the paper S k r z y c z y ń s k a and R z y m o w s k a (2005).Due to extensive documentation material taking into account the diversity of habitats of the Podlaski Przełom Bugu mesoregion, it was divided into two parts, notably, communities developing primarily on light soils and on cohesive soils.This is a conventional division; this paper presents root crop phytocenoses developing most frequently on light sandy, poorly fertile and usually acid soils.The documentation material comprised 160 phytosociological relevés.

Characteristics of distinguished associations and communities
In root crops of the Podlaski Przełomu Bugu mesoregion, on light, sandy and acid soils, the occurrence of patches of two associations and a community from the Panico-Setarion alliance was found.These are Digitarietum ischaemi and Echinochloo-Setarietum and the Setaria pumila-Setaria viridis community.
Digitarietum ischaemi R. Tx. et Prsg (1942) 1950 Typical patches of this association developed on sandy, acid and poorly fertile soils.Such phytocenoses developed both on dry and excessively wetted soils, what formed the basis for distinguishing the typical variant and the variant with Gnaphalium uliginosum.
The typical variant of the association was found on alluvial soils and on brown leached soils classified as the very weak and weak rye complex.It was described based on 25 phytosociological relevés (Tab.1).In these patches, the characteristic species of the association -Digitaria ischaemum -dominated.Setaria pumila also had a large share in them.Setaria viridis occurred often, but with much lower cover.Frequent components of these phytocenoses were also other acidophilous species: Rumex acetosella, Equisetum arvense, Raphanus raphanistrum, Spergula arvensis and Fallopia convolvulus.Their quantitative share was however much smaller compared to the abovementioned weeds.
The wet variant of Digitarietum ischaemi developed most frequently on soils of the weak and good rye complex, as well as the weak cereal and grazing complex.It is demonstrated by 10 phytosociological relevés (Tab.1).These patches were characterised by larger cover with Digitaria ischaemum and Setaria viridis, as well as the presence of hygrophilous species.Gnaphalium uliginosum and Juncus bufonius dominated among them.Agropyron repens also occurred there more frequently than in the typical phytocenoses and with much larger cover.
The Digitarietum ischaemi association was composed of 58 species (40 in the typical variant and 45 in the variant with Gnaphalium uliginosum).In one relevé, 10 -16 species (on the average 12) occurred in the typical patches and 11 -27 (on the average 18) in the patches of the variant with Gnaphalium uliginosum.

Setaria pumila-Setaria viridis community
The occurrence of patches of the Setaria pumila--Setaria viridis community, characterised by a large share of distinguishing species, was noted in root crops of the study area.It is documented by 20 phytosociological relevés (Tab.2).The variation of soil moisture conditions of the habitats on which such phytocenoses were noted divides them into the typical form and the form with a share of hygrophilous species.Patches typical for this community developed on sandy soils classified most frequently as the weak rye complex.Apart from the distinguishing species with high permanence and large cover, the following were noted in them: Chenopodium album, Raphanus raphanistrum, Equisetum arvense and Fallopia convolvulus.
The form with a share of hygrophilous species was distinguished by the occurrence of a numerous group of species, indicating excessive wetting of the habitats.Gnaphalium uliginosum was encountered most frequently among them.On the other hand, Stachys palustris, Polygonum amphibium andJuncus bufonius occurred less frequently, but with large cover.These phytocenoses were more weed infested than the typical patches.Agropyron repens, Artemisia vulgaris, Chenopodium album, Viola arvensis, Matricaria maritima ssp.inodora, Sonchus arvensis, Stellaria media and Cirsium arvense, among others, reached in them larger cover and often higher permanence.But the share of acidophilous species, such as Raphanus raphanistrum, Spergula arvensis, Anthemis arvensis, Rumex acetosella and other, decreased.
The community was made up of 78 species (47 composed the typical form and 70 composed the form with a share of hygrophilous species).The number of species in one relevé ranged, respectively, from 11 to 23 (on the average 16) and from 16 to 29 (on the average 23).

Polygono-Chenopodietalia
Chenopodium album Root crops of the Podlaski Przełom Bugu mesoregion were most frequently weed infested by patches of Echinochloo-Setarietum.Among root crop communities, this association demonstrates the greatest internal variation which results from variable trophic and moisture conditions of its habitats.3 subassociations were distinguished in the study area: Echinochloo-Setarietum setarietosum glaucae, Echinochloo-Setarietum typicum and Echinochloo-Setarietum fumarietosum, as well as 12 lower syntaxonomic units.On light soils, patches of Echinochloo-Setarietum setarietosum glaucae and Echinochloo-Setarietum typicum were noted.Within these two subassociations, 9 lower syntaxa were distinguished.
The poorest habitats were occupied by phytocenoses of Echinochloo-Setarietum setarietosum glaucae.The typical variant of this subassociation is documented by 20 phytosociological relevés (tab.3).Such phytocenoses developed on soils classified as the following rye complexes: weak, good and very good.Out of the species characteristic for the association, Echinochloa crus-galli occurred in large numbers in these patches.
Raphanus raphanistrum was also a permanent species of these phytocenoses, but it was noted with much lower cover.Apart from Barnyardgrass, Setaria pumila dominated in the patches.The other distinguishing species had much smaller cover.Among them, Setaria viridis and Spergula arvensis were noted most frequently, less frequently Rumex acetosella and Scleranthus annuus.
In addition, Chenopodium album, Anthemis arvensis, Equisetum arvense and Fallopia convolvulus were also encountered often and with large cover.
The variant with Juncus bufonius is demonstrated by 10 phytosociological relevés (Tab.3).Such phytocenoses were noted on different soil types.They were most frequently soils formed from clay-bedded loamy sands.In these patches, Echinochloa crus-galli occurred with smaller intensity than in the typical patches, Raphanus raphanistrum was rarely noted.But they were dominated by Setaria pumila.Hygrophilous species, in particular Juncus bufonius and Gnaphalium uliginosum, were also noted in them frequently and with large cover.The share of other species in the formation of these communities was similar as in the typical variant; however, a more frequent occurrence of Stellaria media was observed.
The association was composed of 82 species (60 in the typical variant and 61 in the variant with Juncus bufonius).The number of species in one relevé ranged from 10 to 23 (on the average, it was 17) in the typical variant and from 17 to 28 (on the average 22) in the variant with Juncus bufonius.
A part of the patches of Echinochloo-Setarietum setarietosum glaucae, both in the typical variant and in the wet variant, was dominated by Digitaria ischaemum, therefore, a subvariant with this species was distinguished in both the variants (Tab.4).Apart from the mass occurrence of smooth crabgrass, acidophilous species distinguishing this subassociation, such as Spergula arvensis, Scleranthus annuus and Rumex acetosella, were noted in these patches more frequently and with larger cover.In the wet variant, apart from the hygrophilous species, Chenopodium album also had a large share, compared to the typical variant; Polygonum lapathifolium ssp.lapathifolium was also encountered more frequently and with larger cover.
These were much poorer phytocenoses, in terms of the species composition, compared to the above discussed.In total, 57 species were noted in them (only 34 species in the typical variant and 49 in the variant with Juncus bufonius).The number of species in one relevé ranged, respectively, from 10 to 18 (on the average 16) and from 11 to 29 (on the average 18).
Echinochloo-Setarietum typicum occurred commonly across the whole area of the Podlaski Przełom Bugu mesoregion.The variability of trophic and soil moisture conditions was manifested by the floristic diversity of its patches.
Typical patches developed in potato and beet crops on alluvial, pseudo-podsolic and brown leached soils classified as the following rye complexes: very good, good and weak, as well as as the good wheat complex.Phytocenoses of the typical variant are demonstrated by 15 phytosociological relevés (Tab.5).Echinochloa crus-galli also occurred in large numbers in them, whereas Raphanus raphanistrum was found less frequently and with much smaller cover.The following nitrophilous weeds: Chenopodium album and Galinsoga parviflora, also had a large share in them.Setaria viridis, Equisetum arvense, Anthemis arvensis, Fallopia convolvulus and others were also noted frequently, but with less intensity.
The variant with Juncus bufonius was encountered on different soil types most frequently classified as cereal and grazing complexes.It is demonstrated by 15 phytosociological relevés (Tab.5).These patches, similarly to the typical ones, were dominated by Barnyardgrass.The physiognomy of these phytocenoses was determined to a large extent by hygrophilous species.Among them, Juncus bufonius occurred in large numbers, Gnaphalium uliginosum, Plantago intermedia, Mentha arvensis and Ranunculus repens also had a large share.Nitrophilous weeds, such as Chenopodium album, Polygonum lapathifolium ssp.lapathifolium, Stellaria media, Polygonum persicaria, were a numerous group of species in the phytocenoses of the variant with Juncus bufonius.
Juncus bufonius   A part of patches of Echinochloo-Setarietum typicum was marked by the numerous occurrence of Oxalis stricta, and they were classified as a subvariant with this species.Such phytocenoses developed on different soil types, quite frequently these were soils formed from ordinary dusty soils.They were encountered more frequently in excessively wetted habitats.This subvariant is demonstrated by 25 phytosociological relevés, 10 for the typical variant and 15 for the wet variant with Gnaphalium uliginosum (Tab.6).
The patches of the subvariant with Oxalis stricta, similarly to the typical variant, were dominated by Echinochloa crus-galli.Nitrophilous species: Chenopodium album (especially in the typical variant), Stellaria media, Galinsoga parviflora, Polygonum lapathifolium ssp.lapathifolium, also had a very large share in them.In the wet variant, Gnaphalium uliginosum, Plantago intermedia, Stachys palustris, and locally Mentha arvensis and Potentilla anserine, occurred most frequently and with the largest cover.
These phytocenoses were floristically rich; they were composed of 120 species (78 in the typical variant and 103 in the wet variant).The number of species in one relevé ranged, respectively, from 10 to 34 (on the average 23) and from 20 to 42 (on the average 29).

DISCUSSION
In root crops on light soils of the Podlaski Przełom Bugu mesoregion, two associations were distinguished: Digitarietum ischaemi, Echinochloo-Setarietum and the Setaria pumila-Setaria viridis community.The internal variation of the distinguished communities proves the diversity of habitat conditions.
Most frequently, the studied plantations were covered by patches of Echinochloo-Setarietum.The great floristic variation of the phytocenoses of this association and their frequent occurrence result from a wide ecological amplitude of the characteristic species of this association.Echinochloo-Setarietum is the most wide--spread association among root crops in Poland.It was reported, inter alia, from Jura Krakowska (Kraków Jurassic area) (K o r n a ś , 1950), from the Lubelszczyzna region Fijałkowski (1967), from Równina Piotrkowska (Piotrków Plain) (Wa r c h o l i ń s k a , 1974), from Pasmo Przedborsko-Małogoskie (Przedborsko-Małogoskie Range) (Wnuk, 1976), from Wał Trzebnicki (Trzebnica Morraine Belt) (A n i o ł -K w i a t k o w s k a , 1990), from Wysoczyzna Siedlecka (Siedlce Plateau) (S k r z y c z y ń s k a , 1994).The diversity of habitats affects changes in the floristic composition of the patches of this association.Such variability is described by: Wa r c h o l i ń s k a (1974( ), Wnuk (1976)), A n i o ł --K w i a t k o w s k a (1990), S k r z y c z y ń s k a (1994) and others.
The poorest habitats in the study area were occupied by the phytocenoses of Digitarietum ischaemi.They occurred on poor and acid sandy soils in various moisture conditions.The composition and structure of typical phytocenoses of Digitarietum ischaemi in root crops of the Podlaski Przełom Bugu mesoregion do not differ from those reported from other areas of the country (Wa r c h o l i ń s k a , 1974; S i c i ń s k i ; 1974, W n u k , 1 9 7 6 , A n i o ł -K w i a t k o w s k a , 1 9 9 0 , S k r z y c z y ń s k a , 1994, W ę g r z y n e k , 2005 et al.).Due to specific habitat conditions (water and nutrient deficiency, excess heat and strong acidification) on which patches of Digitarietum ischaemi are encountered, the wet variant of this association was rarely distinguished (A n i o ł -K w i a t k o w s k a , 1990, S i c i ń s k i , 2003).
In root crops, contrary to cereal crops, impoverished phytocenoses are found less frequently.It results, inter alia, from different ways of spreading of weeds in these crop groups, as well as from the intensity of chemical treatment.In cereal crops, speirchoric species are easily eliminated by cleaning of seed material, whereas in root crops, organic fertilisation and insufficient herbicide control on the studied plantations result in a strong development of weed infestation, especially secondary weed infestation.
The Setaria pumila-Setaria viridis community corresponds in its floristic composition to species-poor phytocenoses from the Panico-Setarion alliance described by Węgrzynek (2005).However, within the area of the Podlaski Przełom Bugu mesoregion, Setaria pumila and Setaria viridis had a markedly larger share in the patches of this community.Similar communities from other regions of Poland were reported by: W n u k (1989), W n u k et al. (1989).

(
Comments): (numbers after of species inform about numbers of picture in the table), (withered top leaves).a : m i e s i ą c m o n t

. Setaria glauca-Setaria viridis
: (numbers after of species inform about numbers of picture in the table), z.n (withered top leaves)